Currently: A very weak low pressure system was over central VA and a reinforcing shot of cold air was moving through central PA. This combo is generating a few rain and snow showers, but the majority of the activity will remain to our south.
Tonight: Clearing and cold, as cold air advection commences. Guidance is pretty acceptable, so a split is preferred. Lows should range from the low 20s in the NW hills to near 30 near Mystic Seaport/SE Coast.
Tomorrow: Mostly ineffective sunshine, as a bitter wind ushers in cold air straight from the Arctic. It will feel more like late January rather than mid March. High temperatures should only range from the upper 30s to near 40. A few low 40s could pop up in the CT Valley.
Tomorrow Night/Saturday: Cold air will settle in tomorrow night, as temperatures once again range from the low 20s in the NW Hills to upper 20s along the south coast. It won't be all that much warmer on Saturday, with temperatures only a degree or two warmer than those of Friday.
Long Term: Sunday will be even colder than Saturday. High temperatures probably won't even reach 40 anywhere in the state! Sunday morning will have a midwinter feel, with low temperatures ranging from 15 to 20, with a few readings even as low as the low teens in the NW Hills!
Monday will be a bit warmer, with guidance temperatures generally accepted- a few degrees warmer than Sunday.
Attention then turns to a potential coastal low, which could deliver a big punch of wintry weather. Right now, models differ on the details with the system, but this is to be expected at this range. The UKMET phases the system so much that there would be precipitation type issues for most of the state. While the UKMET office does not offer us very much details regarding this system, as to when the precipitation might change over, etc, you would have to figure that since the model shows a low pressure system over Philadelphia, that there would have to be a changeover at some point.
The ECMWF model, the European model, suppresses the storm so that most precipitation stays south of New York City, although if anything fell here, it would be snow.
The GFS model is actually the middle ground at this time. The evolution on this afternoon's 12Z GFS is actually a classic nor'easter evolution, which would produce a major snowfall for much of the area, especially the southern half of the state. The GFS model is often maligned in the meteorological community for not being very consistent, but it actually did a decent job with the last storm. It did not really pick up on any banding features real well, but this is one thing that the GFS will never do, because it has coarser resolution than the other global models. That being said, this upcoming storm does not look like one that will feature intense banding and such a disparity between "winners and losers" with regards to snowfall. Of course, there are always variances in QPF over certain areas, but this event appears to be a more widespread precipitation producer, rather than one with extreme banding and huge differences over a few miles.
The GGEM, the Canadian model, is in between the ECMWF and GFS, but closer to the GFS. This brings the significant snows up to the south coast and not much north of there. For now, this forecast will have a slight favoring towards the GFS, in an attempt to blend all models minus the ECMWF. The ECMWF model really is a shell of its former self and is no longer as good as it used to be. The ECMWF and GGEM Ensemble models look very much like the GGEM model, while the GFS Ensembles look close to the regular GFS, but a slight step towards the UKMET. If I had to put a model percentage of usage for this forecast, I'd go 50% GFS, 30% GGEM, 20% UKMET, and throw out this particular run of the ECMWF.
Timing has also slowed a bit- what appeared to be a Monday-Tuesday event has now shifted to a Tuesday-Wednesday event. This is likely a function of the -NAO, as this tends to slow down the flow overall. So this could continue to get a little slower, and if the GFS' evolution is correct, snow showers and squalls could linger into Thursday!
One note of caution: Models are not in agreement yet as to whether this will be just one strong wound up storm, or as many as 3 different lows. From my experience as a forecaster, this could be a warning sign that one or more operational models could key on the wrong wave and alter the final outcome. What is best to say right now at this juncture is that it does appear that yet another major snowstorm will affect parts of the Northeastern United States!
Yet another shot of Arctic air could move into the state beyond this low. Looking into the long range, there may finally be slow signs of spring showing up on the long range guidance (although despite what the calendar shows I might urge a little caution with that, since at this time, it was originally supposed to be much above normal this weekend, and now is clearly not going to be). There could be yet another storm threat in the last week of the month. For now, this would favor further north and west areas. However, this assumption is based on climatology acting like climatology and that has not yet happened this month!
This is the GFS' depiction of the storm. valid midnight Tuesday night. You can see the primary low over SE Ohio and a new developing low off the Delmarva. This is a good setup for heavy overrunning snow converting to coastal storm snows. This map also illustrates High Pressure arching from Quebec to North Dakota. This is yet another reason to throw out the ECMWF solution at this time. The high is NOT in a blocking spot to suppress this system well to the south. Nor is there any feature at the 500 MB level, such as a massive west based -NAO (one that would be too strong for the snow to get this far north), or a suppressive polar vortex. Therefore, the ECMWF guidance is being thrown out this afternoon.
That's all for now.. enjoy your Saint Patrick's Day weekend!